1 .\" Copyright 1995 Robert K. Nichols (Robert.K.Nichols@att.com)
2 .\" Copyright 1999-2005 Kai Mäkisara (Kai.Makisara@kolumbus.fi)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
23 .TH ST 4 2010-09-04 "Linux" "Linux Programmer's Manual"
25 st \- SCSI tape device
28 .B #include <sys/mtio.h>
30 .BI "int ioctl(int " fd ", int " request " [, (void *)" arg3 "]);"
31 .BI "int ioctl(int " fd ", MTIOCTOP, (struct mtop *)" mt_cmd );
32 .BI "int ioctl(int " fd ", MTIOCGET, (struct mtget *)" mt_status );
33 .BI "int ioctl(int " fd ", MTIOCPOS, (struct mtpos *)" mt_pos );
38 driver provides the interface to a variety of SCSI tape devices.
39 Currently, the driver takes control of all detected devices of type
40 \(lqsequential-access\(rq.
43 driver uses major device number 9.
45 Each device uses eight minor device numbers.
46 The lowermost five bits
47 in the minor numbers are assigned sequentially in the order of
49 In the 2.6 kernel, the bits above the eight lowermost bits are
50 concatenated to the five lowermost bits to form the tape number.
51 The minor numbers can be grouped into
52 two sets of four numbers: the principal (auto-rewind) minor device numbers,
54 and the \(lqno-rewind\(rq device numbers,
56 Devices opened using the principal device number will be sent a
58 command when they are closed.
59 Devices opened using the \(lqno-rewind\(rq device number will not.
60 (Note that using an auto-rewind device for positioning the tape with,
61 for instance, mt does not lead to the desired result: the tape is
62 rewound after the mt command and the next command starts from the
63 beginning of the tape).
65 Within each group, four minor numbers are available to define
66 devices with different characteristics (block size, compression,
68 When the system starts up, only the first device is available.
69 The other three are activated when the default
70 characteristics are defined (see below).
71 (By changing compile-time
72 constants, it is possible to change the balance between the maximum
73 number of tape drives and the number of minor numbers for each
75 The default allocation allows control of 32 tape drives.
76 For instance, it is possible to control up to 64 tape drives
77 with two minor numbers for different options.)
79 Devices are typically created by:
83 mknod \-m 666 /dev/st0 c 9 0
84 mknod \-m 666 /dev/st0l c 9 32
85 mknod \-m 666 /dev/st0m c 9 64
86 mknod \-m 666 /dev/st0a c 9 96
87 mknod \-m 666 /dev/nst0 c 9 128
88 mknod \-m 666 /dev/nst0l c 9 160
89 mknod \-m 666 /dev/nst0m c 9 192
90 mknod \-m 666 /dev/nst0a c 9 224
94 There is no corresponding block device.
96 The driver uses an internal buffer that has to be large enough to hold
97 at least one tape block.
98 In kernels before 2.1.121, the buffer is
99 allocated as one contiguous block.
100 This limits the block size to the
101 largest contiguous block of memory the kernel allocator can provide.
102 The limit is currently 128 kB for 32-bit architectures and
103 256 kB for 64-bit architectures.
104 In newer kernels the driver
105 allocates the buffer in several parts if necessary.
107 maximum number of parts is 16.
108 This means that the maximum block size
109 is very large (2 MB if allocation of 16 blocks of 128 kB succeeds).
111 The driver's internal buffer size is determined by a compile-time
112 constant which can be overridden with a kernel startup option.
113 In addition to this, the driver tries to allocate a larger temporary
114 buffer at run time if necessary.
115 However, run-time allocation of large
116 contiguous blocks of memory may fail and it is advisable not to rely
117 too much on dynamic buffer allocation with kernels older than 2.1.121
118 (this applies also to demand-loading the driver with kerneld or kmod).
120 The driver does not specifically support any tape drive brand or
122 After system start-up the tape device options are defined by
124 For example, if the drive firmware selects fixed-block mode,
125 the tape device uses fixed-block mode.
127 be changed with explicit
129 calls and remain in effect when the device is closed and reopened.
130 Setting the options affects both the auto-rewind and the nonrewind
133 Different options can be specified for the different devices within
134 the subgroup of four.
135 The options take effect when the device is
137 For example, the system administrator can define
138 one device that writes in fixed-block mode with a certain block size,
139 and one which writes in variable-block mode (if the drive supports
144 if they are supported by the drive.
145 (Note that the tape partitions
146 have nothing to do with disk partitions.
147 A partitioned tape can be
148 seen as several logical tapes within one medium.)
149 Partition support has to be enabled with an
152 location is preserved within each partition across partition changes.
153 The partition used for subsequent tape operations is
156 The partition switch is executed together with
157 the next tape operation in order to avoid unnecessary tape
159 The maximum number of partitions on a tape is defined by a
160 compile-time constant (originally four).
161 The driver contains an
163 that can format a tape with either one or two partitions.
167 is usually created as a hard or soft link to the default tape device
170 Starting from kernel 2.6.2, the driver exports in the sysfs directory
171 .I /sys/class/scsi_tape
172 the attached devices and some parameters assigned to the devices.
174 The driver supports operation in both fixed-block mode and
175 variable-block mode (if supported by the drive).
176 In fixed-block mode the drive
177 writes blocks of the specified size and the block size is not
178 dependent on the byte counts of the write system calls.
179 In variable-block mode one tape block is written for each write call
181 count determines the size of the corresponding tape block.
183 the blocks on the tape don't contain any information about the
184 writing mode: when reading, the only important thing is to use
185 commands that accept the block sizes on the tape.
187 In variable-block mode the read byte count does not have to match
188 the tape block size exactly.
189 If the byte count is larger than the
190 next block on tape, the driver returns the data and the function
191 returns the actual block size.
192 If the block size is larger than the
193 byte count, the requested amount of data from the start of the block
194 is returned and the rest of the block is discarded.
196 In fixed-block mode the read byte counts can be arbitrary if
197 buffering is enabled, or a multiple of the tape block size if
198 buffering is disabled.
199 Kernels before 2.1.121 allow writes with
200 arbitrary byte count if buffering is enabled.
202 (kernel before 2.1.121 with buffering disabled or newer kernel) the
203 write byte count must be a multiple of the tape block size.
205 In the 2.6 kernel, the driver tries to use direct transfers between the user
206 buffer and the device.
207 If this is not possible, the driver's internal buffer
209 The reasons for not using direct transfers include improper alignment
210 of the user buffer (default is 512 bytes but this can be changed by the HBA
211 driver), one of more pages of the user buffer not reachable by the
214 A filemark is automatically written to tape if the last tape operation
215 before close was a write.
217 When a filemark is encountered while reading, the following
219 If there are data remaining in the buffer when the filemark
220 is found, the buffered data is returned.
221 The next read returns zero
223 The following read returns data from the next file.
225 recorded data is signaled by returning zero bytes for two consecutive
227 The third read returns an error.
229 The driver supports three
232 Requests not recognized by the
234 driver are passed to the
237 The definitions below are from
238 .IR /usr/include/linux/mtio.h :
239 .SS "MTIOCTOP \(em Perform a tape operation"
241 This request takes an argument of type
242 .IR "(struct mtop *)" .
243 Not all drives support all operations.
244 The driver returns an
246 error if the drive rejects an operation.
250 /* Structure for MTIOCTOP \- mag tape op command: */
252 short mt_op; /* operations defined below */
253 int mt_count; /* how many of them */
258 Magnetic Tape operations for normal tape use:
269 Reposition the tape to the EOT side of the last filemark.
274 records (tape blocks).
282 Enable compression of tape data within the drive if
284 is nonzero and disable compression if
287 This command uses the MODE page 15 supported by most DATs.
290 Go to the end of the recorded media (for appending files).
294 With 2.6 kernel, short erase (mark tape empty) is performed if the
296 Otherwise long erase (erase all) is done.
307 Reposition the tape to the BOT side of the last filemark.
312 records (tape blocks).
320 Execute the SCSI load command.
321 A special case is available for some HP
326 .B MT_ST_HPLOADER_OFFSET
327 plus a number, the number is
328 sent to the drive to control the autoloader.
331 Lock the tape drive door.
334 Format the tape into one or two partitions.
337 is nonzero, it gives the size of the first partition and the second
338 partition contains the rest of the tape.
341 is zero, the tape is formatted into one partition.
342 This command is not allowed for a drive unless the partition support
343 is enabled for the drive (see
344 .BR MT_ST_CAN_PARTITIONS
348 No op\(emflushes the driver's buffer as a side effect.
349 Should be used before reading status with
353 Rewind and put the drive off line.
365 Seek to the tape block number specified in
367 This operation requires either a SCSI-2 drive that supports the
369 command (device-specific address)
370 or a Tandberg-compatible SCSI-1 drive (Tandberg, Archive
371 Viper, Wangtek, ...).
372 The block number should be one that was previously returned by
374 if device-specific addresses are used.
377 Set the drive's block length to the value specified in
379 A block length of zero sets the drive to variable block size mode.
382 Set the tape density to the code in
384 The density codes supported by a drive can be found from the drive
388 The active partition is switched to
390 The partitions are numbered from zero.
391 This command is not allowed for
392 a drive unless the partition support is enabled for the drive (see
393 .B MT_ST_CAN_PARTITIONS
397 Execute the SCSI unload command (does not eject the tape).
400 Unlock the tape drive door.
412 Magnetic Tape operations for setting of device options (by the superuser):
415 Set various drive and driver options according to bits encoded in
417 These consist of the drive's buffering mode, a set of Boolean driver
418 options, the buffer write threshold, defaults for the block size and
419 density, and timeouts (only in kernels 2.1 and later).
420 A single operation can affect only one item in the list above (the
421 Booleans counted as one item.)
423 A value having zeros in the high-order 4 bits will be used to set the
424 drive's buffering mode.
425 The buffering modes are:
428 The drive will not report
430 status on write commands until the data
431 blocks are actually written to the medium.
435 status on write commands as soon as all the
436 data has been transferred to the drive's internal buffer.
440 status on write commands as soon as (a) all
441 the data has been transferred to the drive's internal buffer, and
442 (b) all buffered data from different initiators has been successfully
443 written to the medium.
446 To control the write threshold the value in
448 must include the constant
449 .BR MT_ST_WRITE_THRESHOLD
450 bitwise ORed with a block count in the low 28 bits.
451 The block count refers to 1024-byte blocks, not the physical block
453 The threshold cannot exceed the driver's internal buffer size (see
456 To set and clear the Boolean options
459 must include one of the constants
461 .BR MT_ST_SETBOOLEANS ,
462 .BR MT_ST_CLEARBOOLEANS ,
464 .BR MT_ST_DEFBOOLEANS
466 whatever combination of the following options is desired.
469 the options can be set to the values
470 defined in the corresponding bits.
472 .BR MT_ST_SETBOOLEANS
473 the options can be selectively set and with
474 .BR MT_ST_DEFBOOLEANS
477 The default options for a tape device are set with
478 .BR MT_ST_DEFBOOLEANS .
479 A nonactive tape device (e.g., device with
480 minor 32 or 160) is activated when the default options for it are
481 defined the first time.
482 An activated device inherits from the device
483 activated at start-up the options not set explicitly.
485 The Boolean options are:
488 .BR MT_ST_BUFFER_WRITES " (Default: true)"
489 Buffer all write operations in fixed-block mode.
490 If this option is false and the drive uses a fixed block size, then
491 all write operations must be for a multiple of the block size.
492 This option must be set false to write reliable multivolume archives.
495 .BR MT_ST_ASYNC_WRITES " (Default: true)"
496 When this option is true, write operations return immediately without
497 waiting for the data to be transferred to the drive if the data fits
498 into the driver's buffer.
499 The write threshold determines how full the buffer must be before a
500 new SCSI write command is issued.
501 Any errors reported by the drive will be held until the next
503 This option must be set false to write reliable multivolume archives.
505 .BR MT_ST_READ_AHEAD " (Default: true)"
506 This option causes the driver to provide read buffering and
507 read-ahead in fixed-block mode.
508 If this option is false and the drive uses a fixed block size, then
509 all read operations must be for a multiple of the block size.
511 .BR MT_ST_TWO_FM " (Default: false)"
512 This option modifies the driver behavior when a file is closed.
513 The normal action is to write a single filemark.
514 If the option is true the driver will write two filemarks and
515 backspace over the second one.
518 This option should not be set true for QIC tape drives since they are
519 unable to overwrite a filemark.
520 These drives detect the end of recorded data by testing for blank tape
521 rather than two consecutive filemarks.
522 Most other current drives also
523 detect the end of recorded data and using two filemarks is usually
524 necessary only when interchanging tapes with some other systems.
526 .BR MT_ST_DEBUGGING " (Default: false)"
527 This option turns on various debugging messages from the driver
528 (effective only if the driver was compiled with
532 .BR MT_ST_FAST_EOM " (Default: false)"
533 This option causes the
535 operation to be sent directly to the
536 drive, potentially speeding up the operation but causing the driver to
537 lose track of the current file number normally returned by the
542 is false the driver will respond to an
544 request by forward spacing over files.
546 .BR MT_ST_AUTO_LOCK " (Default: false)"
547 When this option is true, the drive door is locked when the device is
548 opened and unlocked when it is closed.
550 .BR MT_ST_DEF_WRITES " (Default: false)"
551 The tape options (block size, mode, compression, etc.) may change
552 when changing from one device linked to a drive to another device
553 linked to the same drive depending on how the devices are
555 This option defines when the changes are enforced by the
556 driver using SCSI-commands and when the drives auto-detection
557 capabilities are relied upon.
558 If this option is false, the driver
559 sends the SCSI-commands immediately when the device is changed.
561 option is true, the SCSI-commands are not sent until a write is
563 In this case the drive firmware is allowed to detect the
564 tape structure when reading and the SCSI-commands are used only to
565 make sure that a tape is written according to the correct specification.
567 .BR MT_ST_CAN_BSR " (Default: false)"
568 When read-ahead is used, the tape must sometimes be spaced backward to the
569 correct position when the device is closed and the SCSI command to
570 space backward over records is used for this purpose.
572 drives can't process this command reliably and this option can be used
573 to instruct the driver not to use the command.
574 The end result is that,
575 with read-ahead and fixed-block mode, the tape may not be correctly
576 positioned within a file when the device is closed.
578 default is true for drives supporting SCSI-3.
580 .BR MT_ST_NO_BLKLIMS " (Default: false)"
581 Some drives don't accept the
582 .B "READ BLOCK LIMITS"
584 If this is used, the driver does not use the command.
586 that the driver can't check before sending commands if the selected
587 block size is acceptable to the drive.
589 .BR MT_ST_CAN_PARTITIONS " (Default: false)"
590 This option enables support for several partitions within a
592 The option applies to all devices linked to a drive.
594 .BR MT_ST_SCSI2LOGICAL " (Default: false)"
595 This option instructs the driver to use the logical block addresses
596 defined in the SCSI-2 standard when performing the seek and tell
597 operations (both with
601 commands and when changing tape
603 Otherwise the device-specific addresses are used.
604 It is highly advisable to set this option if the drive supports the
605 logical addresses because they count also filemarks.
607 drives that only support the logical block addresses.
609 .BR MT_ST_SYSV " (Default: false)"
610 When this option is enabled, the tape devices use the SystemV
612 Otherwise the BSD semantics are used.
614 difference between the semantics is what happens when a device used
615 for reading is closed: in System V semantics the tape is spaced forward
616 past the next filemark if this has not happened while using the
618 In BSD semantics the tape position is not changed.
620 .BR MT_NO_WAIT " (Default: false)"
621 Enables immediate mode (i.e., don't wait for the command to finish) for some
622 commands (e.g., rewind).
629 mt_cmd.mt_op = MTSETDRVBUFFER;
630 mt_cmd.mt_count = MT_ST_BOOLEANS |
631 MT_ST_BUFFER_WRITES | MT_ST_ASYNC_WRITES;
632 ioctl(fd, MTIOCTOP, mt_cmd);
637 The default block size for a device can be set with
639 and the default density code can be set with
640 .BR MT_ST_DEFDENSITY .
641 The values for the parameters are or'ed
642 with the operation code.
644 With kernels 2.1.x and later, the timeout values can be set with the
647 ORed with the timeout in seconds.
648 The long timeout (used for rewinds and other commands
649 that may take a long time) can be set with
650 .BR MT_ST_SET_LONG_TIMEOUT .
651 The kernel defaults are very long to
652 make sure that a successful command is not timed out with any
654 Because of this the driver may seem stuck even if it is only
655 waiting for the timeout.
656 These commands can be used to set more
657 practical values for a specific drive.
658 The timeouts set for one device
659 apply for all devices linked to the same drive.
661 Starting from kernels 2.4.19 and 2.5.43, the driver supports a status
662 bit which indicates whether the drive requests cleaning.
663 The method used by the
664 drive to return cleaning information is set using the
667 If the value is zero, the cleaning
669 If the value is one, the TapeAlert data defined
670 in the SCSI-3 standard is used (not yet implemented).
673 If the lowest eight bits are >= 18, bits from the extended
675 The bits 9-16 specify a mask to select the bits
676 to look at and the bits 17-23 specify the bit pattern to look for.
677 If the bit pattern is zero, one or more bits under the mask indicate
678 the cleaning request.
679 If the pattern is nonzero, the pattern must match
680 the masked sense data byte.
681 .SS "MTIOCGET \(em Get status"
683 This request takes an argument of type
684 .IR "(struct mtget *)" .
688 /* structure for MTIOCGET \- mag tape get status command */
692 /* the following registers are device dependent */
696 /* The next two fields are not always used */
703 The header file defines many values for
705 but the current driver reports only the generic types
707 (Generic SCSI-1 tape)
710 (Generic SCSI-2 tape).
712 contains the current tape partition number.
714 reports the drive's current settings for block size (in the low 24
715 bits) and density (in the high 8 bits).
716 These fields are defined by
717 .BR MT_ST_BLKSIZE_SHIFT ,
718 .BR MT_ST_BLKSIZE_MASK ,
719 .BR MT_ST_DENSITY_SHIFT ,
721 .BR MT_ST_DENSITY_MASK .
723 reports generic (device independent) status information.
724 The header file defines macros for testing these status bits:
727 \fBGMT_EOF\fP(\fIx\fP):
728 The tape is positioned just after a filemark
729 (always false after an
733 \fBGMT_BOT\fP(\fIx\fP):
734 The tape is positioned at the beginning of the first file (always false
739 \fBGMT_EOT\fP(\fIx\fP):
740 A tape operation has reached the physical End Of Tape.
742 \fBGMT_SM\fP(\fIx\fP):
743 The tape is currently positioned at a setmark
744 (always false after an
748 \fBGMT_EOD\fP(\fIx\fP):
749 The tape is positioned at the end of recorded data.
751 \fBGMT_WR_PROT\fP(\fIx\fP):
752 The drive is write-protected.
753 For some drives this can also mean that the drive does not support
754 writing on the current medium type.
756 \fBGMT_ONLINE\fP(\fIx\fP):
759 found the drive with a tape in place and ready for operation.
761 \fBGMT_D_6250\fP(\fIx\fP), \fBGMT_D_1600\fP(\fIx\fP), \fBGMT_D_800\fP(\fIx\fP):
762 This \(lqgeneric\(rq status information reports the current
763 density setting for 9-track \(12" tape drives only.
765 \fBGMT_DR_OPEN\fP(\fIx\fP):
766 The drive does not have a tape in place.
768 \fBGMT_IM_REP_EN\fP(\fIx\fP):
769 Immediate report mode.
770 This bit is set if there are no guarantees that
771 the data has been physically written to the tape when the write call
773 It is set zero only when the driver does not buffer data and
774 the drive is set not to buffer data.
776 \fBGMT_CLN\fP(\fIx\fP):
777 The drive has requested cleaning.
778 Implemented in kernels since 2.4.19 and 2.5.43.
781 The only field defined in
783 is the recovered error count in the low 16 bits (as defined by
784 .BR MT_ST_SOFTERR_SHIFT
786 .BR MT_ST_SOFTERR_MASK .
787 Due to inconsistencies in the way drives report recovered errors, this
788 count is often not maintained (most drives do not by default report
789 soft errors but this can be changed with a SCSI MODE SELECT command).
791 reports the current file number (zero-based).
792 This value is set to \-1 when the file number is unknown (e.g., after
797 reports the block number (zero-based) within the current file.
798 This value is set to \-1 when the block number is unknown (e.g., after
803 .SS "MTIOCPOS \(em Get tape position"
805 This request takes an argument of type
806 .I "(struct mtpos *)"
807 and reports the drive's notion of the current tape block number,
808 which is not the same as
812 This drive must be a SCSI-2 drive that supports the
814 command (device-specific address)
815 or a Tandberg-compatible SCSI-1 drive (Tandberg, Archive
816 Viper, Wangtek, ... ).
820 /* structure for MTIOCPOS \- mag tape get position command */
822 long mt_blkno; /* current block number */
830 An attempt was made to write or erase a write-protected tape.
831 (This error is not detected during
835 The device is already in use or the driver was unable to allocate a
839 The command parameters point to memory not belonging to the calling
845 had an invalid argument, or a requested block size was invalid.
848 The requested operation could not be completed.
853 is smaller than the next physical block on the tape.
854 (Before 2.2.18 and 2.4.0-test6 the extra bytes have been
858 A write operation could not be completed because the tape reached
866 During opening, the tape device does not exist.
869 An attempt was made to read or write a variable-length block that is
870 larger than the driver's internal buffer.
873 Open is attempted with
877 when the tape in the drive is write-protected.
881 the auto-rewind SCSI tape devices
884 the nonrewind SCSI tape devices
886 .\" The driver has been written by Kai M\(:akisara (Kai.Makisara@metla.fi)
887 .\" starting from a driver written by Dwayne Forsyth.
889 .\" people have also contributed to the driver.
892 When exchanging data between systems, both systems have to agree on
893 the physical tape block size.
894 The parameters of a drive after startup
895 are often not the ones most operating systems use with these
897 Most systems use drives in variable-block mode if the drive
899 This applies to most modern drives, including
900 DATs, 8mm helical scan drives, DLTs, etc.
901 It may be advisable to use
902 these drives in variable-block mode also in Linux (i.e., use
906 at system startup to set the mode), at least when
907 exchanging data with a foreign system.
909 this is that a fairly large tape block size has to be used to get
910 acceptable data transfer rates on the SCSI bus.
914 allow the user to specify the blocking
915 factor on the command line.
916 Note that this determines the physical block
917 size on tape only in variable-block mode.
919 In order to use SCSI tape drives, the basic SCSI driver,
920 a SCSI-adapter driver and the SCSI tape driver must be either
921 configured into the kernel or loaded as modules.
923 driver is not present, the drive is recognized but the tape support
924 described in this page is not available.
926 The driver writes error messages to the console/log.
928 codes written into some messages are automatically translated to text
929 if verbose SCSI messages are enabled in kernel configuration.
931 The driver's internal buffering allows good throughput in fixed-block
937 With direct transfers
938 this is not possible and may cause a surprise when moving to the 2.6
940 The solution is to tell the software to use larger transfers (often
941 telling it to use larger blocks).
942 If this is not possible, direct transfers can be disabled.
944 .\" Copyright \(co 1995 Robert K. Nichols.
946 .\" Copyright \(co 1999-2005 Kai M\(:akisara.
948 .\" Permission is granted to make and distribute verbatim copies of this
949 .\" manual provided the copyright notice and this permission notice are
950 .\" preserved on all copies.
951 .\" Additional permissions are contained in the header of the source file.
956 .I drivers/scsi/README.st
958 .I Documentation/scsi/st.txt
959 (kernel >= 2.6) in the kernel sources contains
960 the most recent information about the driver and its configuration
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